Late Pleistocene heather vole, Phenacomys, on the North Pacific Coast of North America: environments, local extinctions, and archaeological implications

Phenacomys cf. intermedius, the heather vole, is known from three late Pleistocene and early Holocene localities on Vancouver Island, British Columbia, Canada, where they are absent today. This study reports the heather vole specimens from one of these sites, P2 Cave, and provides a human behavioural context for its presence and eventual extirpation as a consequence of changing environments. Heather vole is a cold-adapted rodent. The early Holocene thermal maximum and subsequent development of coastal western hemlock forests contributed to its Vancouver Island extinction without an apparent corresponding range restriction in higher elevation habitats as has been noted elsewhere in Western North America. Tendency for low population densities in closed-canopy forests, antisocial intraspecies behaviours, and limited immigration across fragmented habitats supported local extinction. The absence of heather vole in the modern environment elsewhere along the coasts of British Columbia, Southeast Alaska, and Washington is probably due to similar factors as are highlighted here. Toward environmental reconstruction and the archaeological setting this study suggests that humans are unlikely to have occupied the Vancouver Island area during a hiatus in the vertebrate faunal record including the cold-adapted heather vole from about 19 700 to 14 700 years ago when the Cordilleran Ice Sheet extended west to the continental shelf. Improved environmental conditions for humans occurred both before and after this time. It also suggests that the glacial conditions in which the heather vole occupied Vancouver Island diverge from the Holocene interglacial setting that has seen an expansion of a human presence and of the corresponding archaeological record.